The present application relates to thermally treated expanded perlite and, more particularly, to a light-weight filtration media comprising thermally treated expanded perlite. In accordance with particular embodiments, the present invention relates to thermally treated expanded perlite impregnated with active materials and, more particularly, to a light-weight filtration media comprising expanded perlite thermally impregnated with at least one active mineral, such as calcium, magnesium, aluminum, or iron. In accordance with one aspect of the present invention, the disclosed light-weight filtration media has the capacity to remove microbial matter from an aqueous composition. In accordance with another aspect, the filtration media has the capacity to remove dissolved phosphorus from an aqueous composition containing phosphorus. In accordance with yet another aspect of the present invention, the disclosed light-weight filtration media has the capacity to remove dissolved metals, such as copper, zinc, lead, nickel and cadmium, from an aqueous composition containing dissolved metals. Methods for forming thermally treated expanded perlite and expanded perlite thermally impregnated with active materials are also disclosed.
Widely used as a filtration media to remove particulate matter in stormwater runoff because it is light-weight, cost effective, and environmentally friendly, expanded perlite has some disadvantages that limits its application. Expanded perlite in the dry form carries dusty fines on its surface. When the expanded perlite contacts water, the dusty fines are washed from the surface of the perlite and increase the turbidity of the water. Furthermore, conventional expanded perlite is limited as far as its application as a filtration material because it is friable and is characterized by a low crush strength. Therefore, there is a need in the art for a filtration media comprising expanded perlite in a form that is less friable, contains fewer fines and exhibits improved crush strength.
In addition to its use as a direct filtration media, expanded perlite can also provide a desirable platform for adsorptive filtration media that could be engineered to selectively remove unwanted components from an aqueous composition such as stormwater or wastewater. Because of its siliceous nature, perlite has affinity to some selected actives, one of which is quaternary ammonium chloride, to remove microbial matter in the water. However, the efficacy of conventional expanded perlite to remove microbial matter is significantly reduced by the tendency of the surficial fines to wash away in the water. Moreover, the actives attached to the surficial fines could also be washed away into the water. Accordingly, effectiveness of expanded perlite as a filtration media could be increased by reducing the number of surficial fines on the perlite.
Perlite also has a very low affinity for common active minerals, such as calcium, magnesium, aluminum and iron, which have the capacity to remove dissolved phosphorus from an aqueous composition. It would be beneficial if the expanded perlite could be modified to remove certain components from an aqueous composition.